Fmoc-protected altritol nucleoside phosphoramidite building blocks with adenine, guanine, thymine, uracil, cytosine and 5-methylcytosine as bases have been synthesized. These building blocks were used for the synthesis of altritol nucleic acid (ANA) and chimeric ANA-RNA oligonucleotides. Whilst the yields of oligonucleotides were lower than those obtained with 3'-O-benzoyl-protected altritol building blocks, the excellent compatibility with Pac-RNA chemistry for the synthesis of chimeric oligonucleotides makes Fmoc a valuable protecting group for the secondary alcohol functions of the sugar moieties of nucleosides for oligonucleotide synthesis. ((c) Wiley-VCH Verlag GmbH & Co.